1. Field
This invention relates to a fuel cell device.
2. Related Art
In a fuel cell having a cell stack composed of multiple stacked unit cells, the cell stack is fastened under a predetermined load to a stacking structure, for maintaining the stacking structure. Referring to a fuel cell described in JP2008-041367A, for example, a spring module is arranged on the side of one end surface of a cell stack so as to be in contact with the cell stack. A predetermined load is applied to the spring module in a direction toward the cell stack, thereby maintaining the stacking structure of the cell stack. In this fuel cell, a female screw is formed in an end plate arranged outside the spring module in a stacking direction. A screw is inserted in this female screw from outside to make the tip of the inserted screw contact the spring module, thereby applying the predetermined load to the spring module continuously. The fuel cell is generally housed in a case. Thus, inserting a screw in a female screw formed in the case instead of the female screw in the end plate also enables adjustment of the load on the cell stack.
If the fuel cell is used in a mobile body such as a vehicle, placing the head of the screw threadedly engaged with the case in a position protruding to the outside from the case is not preferable as collision of the mobile body causes the risk of damaging a member existing near the fuel cell. Thus, it is preferable that a set screw without a screw head be used and this screw be inserted in a manner such that the rear end of the screw in an insertion direction is housed in a position on an inner side relative to a surface of the case. The case is required to be water resistant for the reason of suppressing entry of water into the fuel cell. Thus, in a structure where a female screw is formed in the case and a set screw is to be threadedly engaged in the female screw, using a set screw with an outer circumferential surface coated with a sealing member is an assumed method of assuring sealing performance between the case and the set screw. According to this method, however, the sealing member is removed with the screw thread of the female screw near its insertion hole while the set screw is inserted. In a condition after insertion is completed, the rear end of the set screw is located in a position deeper than the insertion hole. This makes it impossible for the sealing member having been removed with the screw thread near the insertion hole to provide sealing performance. This reduces the sealing performance between the case and the screw, causing the risk of reducing the water resistance of the case. Thus, a technique of suppressing reduction in the water resistance of the case by suppressing reduction in the sealing performance between the case and the screw has been desired. These problems are applied not only to a screw to be used for fixing a pressure plate but is common to various fuel cell devices including screws to be inserted in cases for any different purposes. These problems are also applied to a pin as an insertion member without a screw thread on the outer circumferential surface thereof to be inserted in a case.